1. Field of the Invetion
This invention concerns an antenna device for portable communication equipment and comprising an extendable elongated antenna element which at its lower part comprises a peg element and which is slidable inside a sleeve member between an extended position, where the peg element is mechanically locked in the sleeve member and where simultaneously conductive contact between the sleeve member and the elongated antenna element is established, and a retracted position. The invention also concerns a stopper to be included in the above antenna device.
Such an antenna device is previously known from WO 94/28593, wherein an antenna rod at its lower region is provided with a rigid stopper element which, in the extended position, cooperates with a resilient sleeve member so as to obtain a locking force between these parts.
2. Summary of the Invention
The prior art device is well functioning, however, relatively space-demanding in the axial direction, since the sleeve construction necessarily have relatively large axial dimensions and because the end portion of the stopper element appearing on the outside of the sleeve in the extended position. Further, the prior art solution includes several separate details such as a sleeve, a spring ring for the sleeve, a screw portion and a stopper element, resulting in correspondingly high costs for manufacture, on the one hand of the separate elements and on the other hand for assembly of the elements. The use of several elements also result in accumulated and more widely spread tolerances.
It is an aim of this invention to provide an antenna device of the above mentioned type wherein the prior art problems are eliminated or at least reduced.
This aim is achieved by the peg element being provided with a resilient portion including at least one engagement portion having a contact surface which in the extended position of the antenna rod exerts a locking force against the sleeve member, said engagement portion being provided on a free end of the peg element opposite the antenna rod, and said sleeve member on the inside being provided with an abutment for co-operation, in the extended position of the elongated antenna element, with a corresponding shoulder thereon, said shoulder being located between the contact surface and the upper part of the elongated antenna element.
This way the mutually operating elements--the peg and the sleeve--may simply be constructed as only two elements, thus reducing costs for production and assembly. The sleeve member may be substantially rigid, and therefore it may be produced with reduced dimensions which is of crucial importance in portable communication equipment of today. The aim of space reduction is further achieved by locating the shoulder above the contact surface which is placed at the free end portion of the peg, thus minimizing the axial dimensions of the peg element and consequently of the device as a whole in comparison with the prior art.
Further important features of the invention are reduced weight, possibility of reducing antenna length and reliability.
By providing the resilient portion with one or more bifurcating slot(s) which is (are) arranged in parallel with the axis of the peg element, the resiliency of the resilient portion is easily obtained.
By the contact surface being convex or rounded, i.e. curved in two perpendicular directions, it is assured that the pulling force variation is minimized and this provision also results in a smooth movement when the extended position is established. By the surface being substantially spherical it is achieved that the desired holding force will be obtained also if the peg axis is not perfectly aligned with respect to the sleeve axis.
In an embodiment where the sleeve is cylindrical inside for frictional engagement with the engagement portion(s) a smooth locking action is accomplished and uncomplicated manufacture.
In a preferred aspect of the invention each engagement portion is provided on an axially extended spring acting shank element. This way it is achieved that the looking force exerted by the engagement portion(s) is easily controlled, also with regard to the manufacturing tolerances which otherwise could result in a substantial variation of the locking force and thereby of the pulling force applied to the elongated antenna element by a user for establishing the extended position. This is because the extended shank element which acts as a spring provides limited variation of the engagement force over a reasonable range of the travel length for the engagement portion(s) within which range the manufacturing tolerances are easily included. This feature provides for efficient manufacture and reduces the needs for testing and controlling the function of the finished antenna device and, very important, radically reduces rejection problems. The device according to this aspect of the invention is thus well adapted for production in large series since the control need is eliminated or at least reduced to a minimum. Miniaturization is also made achievable since it provides for controlled forces even though the elements have reduced dimension. As an example it could be mentioned that the diameter of the engagement portion in a particular embodiment is about 2.5 mm.
By the use of a tapering shank element the stress distribution along its length may be optimized and the peg weight further reduced.
By providing the sleeve with a threaded portion for cooperation with a piece of equipment the need for a separate threaded element is eliminated.